Consider adding `IntoParalleliterator` impls for boxed slices, etc.

[JanBeh]

Regarding #1061, it should also be considered to also add IntoParallelIterator traits for Box<[T]>, Rc<[T]>, etc.

This may be a breaking change though. See also Rust issue #59878.

[cuviper]

Yeah, I hesitate to take that chance when the similar impls haven't been added to the standard library either.

[ronnodas]

IntoIterator was added to Box<[T]>, Rc<[T]> and Arc<[T]> in 1.80, so maybe it's reasonable to revisit this?